THE EFFECTS OF PHOSPHORUS AND NITROGEN FERTILIZER ON THE RELATIONSHIP BETWEEN SOIL SALINITY LEVELS AND THE GRAIN YIELD AND PROTEIN CONTENT OF BARLEY GROWN ON STUBBLE LAND

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Abstract
The effect of fertilizer P, N and N-P combined on barley grain yield and protein content when grown on stubble land ranging widely in surface salinity (0-60 cm depth) was tested. Critical salinity levels were calculated from linear regression equations derived from sampling sites with surface salinity levels .gtoreq. 6 mS .cntdot. cm-1. Added P did not appear to affect the salt tolerance of barley. Yield increases due to fertilizer N were reduced rapidly as soil salinity levels increased and in one trial appeared to reduce the tolerance of barley to salinity. Calculated salinity levels at 50% and zero yield of N-fertilized barley were lower than for barley not fertilized with N. Calculated salinity levels at zero yield for the control and P treatments were 18.5 and 15.1 mS .cntdot. cm-1, respectively. These levels compared favorably with values reported in the literature for barley grown on saline fallowed land. Protein content of barley grain increased with an addition of N and with salinity. The latter fact could be largely explained by a strong positive correlation between soil salinity and soil NO3--N levels and to a lesser degree by a reduction in yield with increasing salinity.